Optical components are often mounted on a printed circuit board with other components and into a module housing to form a module. The module is then inserted into a slot in a module card rack. The forward face of the module contains a female optical socket connected to the optical component internal to the module. An optical cable, having a male optical connector at both ends, is used to connect the optical component in the module to an optical component in another module or to/from an optical input/output. One end of the optical cable is plugged into the female optical socket and another end of the optical cable is plugged into the device to which it is to be connected.
There are disadvantages to this set-up. First, the routing and positioning of the optical cable must be managed. Cable management in a large system is not trivial. Second, the module occupies a position in the module card rack which could otherwise be used for another module. Third, the optical component can not easily be replaced in the system since it is mounted to a printed circuit board.
Additionally, the flexibility of the system is limited by the configuration of the available modules. For example, in dense wavelength division multiplexing (DWDM) systems, the modules on the market have a predetermined number of channels which limits the flexibility to provide only a specific number of channels. Also, when there is a need to perform common signal conditioning for all channels at once (e.g. dispersion compensation) or use more optical components to perform the conditioning on a single channel in a multi-channel system (e.g. use a demultiplexer and a single channel dispersion compensator), the modules lack flexibility to easily do so.